1. Field of Invention
This invention relates to the generation of signals in the terahertz frequency range and the detection thereof. In particular, this invention pertains to an ultrafast pulse generator usable for logic operation or as an oscillator or signal carrier for communications.
2. Prior Art
An important aspect of computer cycling speed is the time necessary for communication between logic circuitry and/or memory circuits on a particular chip. By increasing packing density and reducing the physical space between such elements, processing speeds may be increased by reducing the signal path length. A corresponding requirement to attain higher processing speeds is the need for timing circuits which operate at very high frequencies to provide stable clock pulses.
Reference is made to M. B. Ketchen, et al., "Generation of Subpicosecond Electrical Pulses on Coplaner Transmission Lines", Appl. Phys. Lett. 48 (12), 24 Mar. 1986, pp. 751-753. This publication describes techniques to generate ultrashort electrical pulses by photoconductively shorting charged transmission lines and narrow gaps. The technique photoconductively shorts the line by bridging using laser pulses as reported in that article, a transmission line having a design impedance of 100.OMEGA. was made using three parallel 5-.mu.m wide aluminum lines which were separated from each other by 10-.mu.m. That transmission line together with its contact pads was fabricated on an intrinsic silicon on sapphire (SOS) wafer. After fabrication, the wafer was heavily ion implanted to reduce the carrier lifetime. The transmission line was photoconductively shorted utilizing 80 fs laser pulses. The exciting beam had a spot diameter of 10-.mu.m which bridged two of the three parallel transmission lines in a sliding contact arrangement. By utilizing a sampling beam coupled to a multichannel analyzer, subpicosecond electrical pulses were measured having an actual pulse width less than 0.6 ps.
While such demonstrated pulse speed is an improvement over existing technology, further gains are necessary. Specifically, since the laser excitation speed is in the order of 0.08 psec. it is possible to drive switches at higher rates consistent with the input laser switching time. Prior to this invention further gains in cycling speed have not been demonstrated.